The action, which challenges both the state's refusal to allow gay couples to marry and to recognize the marriages of same-sex couples performed in other states, comes after news Wednesday of four couples filing suits against Montana.

"It doesn't matter whether you're first or last," said Nancy Rosenbrahn who along with her partner, Jennie Rosenbrahn, is contesting the state constitutional amendment as an abridgment of their rights under the U.S. Constitution. "It's about sending a message to the country and the Supreme Court: Look at all these states; you can't ignore this."

The lawsuit means that cases now are pending in 30 states with gay-marriage bans. In 19 states and the District of Columbia, same-sex couples already can wed with Oregon and Pennsylvania becoming the latest this week when federal judges struck down their bans and officials decided not to appeal.

South Dakota approved a constitutional ban on same-sex marriage in 2006.

State Attorney General Marty Jackley said it is his responsibility to defend the state constitution and statutes, including a ban on same-sex marriage that 52% of voters approved.

"It is my duty as attorney general, and case law supports, that traditional family values and definitions are determined by state law," Jackley said Wednesday. "And if there is going to be a change, then that change should come from the voters of South Dakota at the ballot box."

"For elected officials, governors or attorney generals, to pick and choose what laws (they) will enforce I think is a tragedy, and is the next step to anarchy," Herbert said. "We have an obligation as a state to defend those laws."

South Dakota state Rep. Steve Hickey, a Sioux Falls Republican and a minister who recently gained publicity over a column posted to Facebook criticizing homosexuality and "gay sex," said the challenge is something "we were waiting for."

"I think (Jackley) will defend our state constitution, but I think this will all eventually come down to five judges in the Supreme Court, which is unfortunate," Hickey said. "This should come down to the people."

Other couples that are a part of the lawsuit are Krystal Cosby and Kaitlynn Hoerner and Barbara and Ashley Wright of Aberdeen, S.D.; Lynn and Monica Serling-Swank of Brandon, S.D.; Jeremy Coller and Clay Schweitzer of Rapid City, S.D.; and Greg Kniffen and Mark Church of Sioux Falls.

Minneapolis-based lawyer Josh Newville is representing the couples and says he's also seriously considering filing a similar challenge in North Dakota. North Dakota's constitutional amendment passed in 2004 with 73% of the vote.

For Nancy Rosenbrahn, 68, filing the ban is not just about the legality of same-sex marriage.

"We want to make noise. By doing this, we have accomplished what we wanted to accomplish," she said. "The reason we decided to take on South Dakota is to open up these conversations."